(b 1) Field of the Invention
This invention relates in general to line-by-line dissection systems of the image of a document or photograph using a solid-state line image sensor, and more particularly it is concerned with mark means placed on the original support plate in a position outside the original supporting zone as a guide for obtaining accurate positioning of an array of light receiving elements of the solid-state line image sensor in a direction perpendicular to the auxiliary scanning direction of the original.
The system described are now widely in use with facsimile transmitters, copying apparatus using a built-in microcomputers, etc. Generally, a line-by-line dissection system comprises irradiating means for irradiating an original, such as document or photograph, with a strip of light of large legth and small width, and a solid-state line image sensor. In this type of system, either the light emanating from the irradiating means or the original is moved relative to the other, to effect auxiliary scanning of the original. In this specification, the auxiliary scanning refers to a scanning effected lengthwise of the original support plate. Another type of line-by-line dissection system comprises irradiating means for irradiating the entire surface of the original, a mirror unit for taking out a portion of the light reflected by the irradiated original as a strip of light, and a solid-state line image sensor. The mirror unit is moved relative to the original to obtain an auxiliary scanning of the original. In both types of system, the light reflected by the original as the auxiliary scanning is carried out is led through a lens to the solid-state line image sensor of the self-scanned type. More specifically, a fragmentary image of the irradiated original or one-line image of the original corresponding to the width of the light receiving elements of the sensor forming an array is transmitted through the lens and formed on the surface of the solid-state line image sensor as an image of a reduced scale. The one-line image of the reduced scale is moved relative to the surface of the solid-state line image sensor in a direction perpendicular to the direction of the longitudinal axis of the line image.
(2) Description of the Prior Art
A line-by-line dissection system used as with a facsimile transmitter is constructed as shown in FIG. 1, for example. A first scanning member 3 comprising a light source 1 and a mirror 2 irradiates an original 5 placed on an original support plate 4 with a strip of light having a larger longitudinal axis than a transverse axis and moves in the direction of an arrow A (auxiliary scanning) while a portion of the light reflected by the original is projected toward a second scanning member 6. The second scanning member 6 which has the reflected light incident thereon reflects the incident light toward an image forming lens 7, while moving in the direction of an arrow B at a velocity which is one half that of the first scanning member 3. The image forming lens 7 on which is incident the light reflected by the original as the first and second scanning members 3 and 6 move causes a portion of the original to be formed as an image of a reduced scale on the light receiving surface of a solid-state line image sensor 8 of the self-scanned type which may comprise a charge coupled device. The solid-state line image sensor 8 comprises a multiplicity of light receiving elements of small area corresponding to picture elements which are arranged in an array for effecting image dissection and conversion of an optical signal into an electrical signal with respect to a straight line portion of the original incident on the light receiving surface of the solid-state line image sensor 8. The electrical signal obtained by the light receiving elements by conversion from the light signal is taken out in chronological sequence as voltage signals each corresponding to one of the light receiving elements. This process of taking out the voltage signals in chronological sequence is referred to as a main scanning. The voltage signals taken out in chronological sequence are coded and forwarded to electronic equipment built in a blotter where the coded signals are restored to their original form to be arrived to the blotter. In the blotter, there are also main scanning and auxiliary scanning directions and the main scanning direction of the blotter is usually perpendicular to the auxiliary scanning direction thereof. This makes it necessary to cause the main scanning direction to be disposed perpendicular to the auxiliary scanning direction in the solid-state line image sensor. If the angle of intersection of the main scanning direction and the auxiliary scanning direction in the blotter is at variance with the corresponding angle in the solid-state line image sensor, the reproduced image of the original would be distorted or inclined.
To enable the direction of the array of the light receiving elements of the solid-state line image sensor or the main scanning direction to be correctly disposed perpendicular to the auxiliary scanning direction, it has hitherto been customary to place, as shown in FIG. 2, a straight line mark 9 or a straight line mark 9' on the original support plate outside an original support zone C in such a manner that the mark 9 extends in a direction perpendicular to the auxiliary scanning direction. An image of the straight line mark 9 would be formed in the vicinity of the solid line image sensor 8 and aid in adjusting the position and inclination of the solid-state line image sensor 8 by bringing the array of light receiving elements into agreement with the image of the straight line mark 9. Whther or not this agreement is obtained could be determined by using an oscilloscope for indicating the voltage signals arranged in chronological sequence, which is referred is as a time-sequential signal.
FIG. 3 shows an example of the positional relation between image 10 of a reduced scale of the straight line mark 9 and the light receiving element array 11 of the solid-state line image sensor 8, obtained when the solid-state line image sensor is tested following its initial setting as a component of the system. It will be noted that in this example the light receiving element array 11 is inclined counterclockwise with respect to the mark image 10 and that the intersection of the two is disposed rightwardly of the center of the light receiving element array 11. In this condition, the output of the solid-state line image sensor 8 is as shown in a broken line in FIG. 4. The output of the solid-state line image sensor 8 will hereinafter be shown in the form of a solid line to facilitate observation of discrete portions of the output signal. Since the width of the image 10 of the reduced scale of the straight line mark 9 is set to be substantially equal to that of the light receiving element array 11, the output of the solid-state line image sensor 8 would become substantially zero when the mark image 10 and the light receiving element array 11 coincide with each other, and the output would be increased in value depending on the degree of coincidence. In FIG. 4, a straight line D represents the output of the solid-state line image sensor 8 obtained when the position of the latter has been adjusted to be in perfect parallel relation to the mark 9. In this figure, the condition of the absence of information (white level) is indicated as being negative and the condition of the presence of information (block level) is indicated as being positive, with the positive output condition being shown in the upper portion of the figure. However, observations of the output condition of the solid-state line image sensor 8 shown in FIG. 4 would provide a basis for judging the position in which the light receiving element array 11 is substantially coincident with the reduced image 10 but could not provide information as to the direction of inclination of the sensor 8 with respect to the mark 9.
Thus, in spite of the expectation that the solid-state line image sensor would be greatly inclined, when the solid-state line image sensor is moved in a direction deemed appropriate in adjusting its position and inclination, the probability that the selected direction is a correct direction would be only 50%. This would make it necessary to carry out an adjusting operation by trial and error until the output becomes uniform in the entire range as indicated by the straight line D. Such operation would increase the time required for mounting the solid-state line image sensors in the production line, thereby reducing production efficiency.
In the prior art, the straight line mark 9 is only one in number. As a result, when a solid-state line image sensor is not parallel to the mark or not correctly positioned with respect to the auxiliary scanning line, when it is initially mounted on the system, the light receiving element array of the sensor will not cross the straight line mark image at all and consequently no output will be produced. In this condition of absence of an output, it would be impossible to determined in which direction the solid-state line image sensor should be moved to bring the light receiving element array into agreement with the straight line mark image.
The position in which the solid-state line image sensor is finally mounted correctly only covers the zone of a straight line mark (actually it is much smaller because it is reduced in scale) and its width corresponds to that of the mark. Thus difficulties would be encountered in effecting adjustments to bring the light receiving element array into alignment with the straight line mark, thereby prolonging the time required for carrying out adjustments.